The investigators propose to test the feasibility of developing a stable isotope-based glomerular filtration rate assay, as further described by their abstract: "Our specific aim is to validate and further develop an innovative method to measure the glomerular filtration rate. We propose using a stable isotope bound to an ideal filtration marker to measure the glomerular filtration rate (GFR) directly from collected serum and/or urine samples using neutron activation technology, a powerful analytical tool. This approach will eliminate both the disadvantages associated with radioactivity and the cumbersome laboratory procedures associated with current nonradioactive methods. Although outside the scope of this project, this technology can also be used to measure glomerular permselectivity and renal blood flow, and can be combined with our proposed glomerular filtration rate assay, thereby consolidating sample collection and data analysis. This approach will provide a glomerular filtration rate assay kit that is safe, easy-to-use, accurate, and cost-effective while providing a diagnostic modality that is versatile for a wide range of situations. Experiments will characterize three ideal filtration markers labeled with three different stable isotopes. Labeled-markers will be tested for labeling efficiency; overall charge; stability to incubation in buffer with temperature variation; stability to challenge in a serum environment; and the sensitivity of detection via neutron activation of each labeled marker will be measured." PROPOSED COMMERCIAL APPLICATION: NOT AVAILABLE